Protection of secondary circuits.



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EL FERGUSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF N EW YORK.

POTECTION OF SECONDARY CIRCUITS.

Specification of Letters Patent.

Patented April 30, 1907.

A Application filed September 9. 1904. Serial No. 223,823. v

useful Improvements in the Protection of Secondary Cir'cu'its, ofwhich the following is a specification. l i

This invention relates to means for protecting electrical lapparatus from abnormal high voltage currents. i

' While my invention is readily-applicable to many cases, it is shown in the drawing,

forming apart of this specification, as ap-' plied to. an alternating'current distributing system in which current at high otential is transmitted to a point near the Vace of consumption and there transforme 'or converted into current of suitable working pressure. 2o

In such systems there is `always more or less dan er of an accidental connection between the' 'gh potential conductors ofthe trans- Qtential circuits thereby raising the secon ary net work to potential of the high voltage conductors I and msequentlykendangering life and apparat-us along the secondary net work. l

In; the drawings Figure .1 shows diagrammatically the high potential windings of three transformers. connected in vdelta to high potential distributing mains; it also shows the secondaries ci these same trans formers connected to low voltage service mains; Fig. 2 is a sectional elevation of an improved vform of film cut-out used in the @und connections of the secondary circuit.

tively primaries of three ste -down transformersfccnnected in delta tot e'high voltage mains 4, 5 and 6. These high voltage mains are provided respectively with ound connections 10, 11 and 12, each of these ground connections being rovided with means for impedng the flow o current.-

In the drawing, I haveshown .these impe# 'dance devices 13 14 and 15 as consisting of non-inductive resistances, but it is obvious loss of a large perl cent. of

that reactances could be usedk for this purpose if such an arrangement appeared desiiable.- i The .resistance of the ground connectionsis suiliciently high to prevent the the current supso that theloss of plied tothe transformers,

`current this Way is comparatively small.

. sulating cup Vsubjected to high voltage In Fii 1, 1,2 and 3 represent respec-V Secondaries 1', 2 and 3', corresponding respectivelyto the primaries 1, 2 and' 3, are connected in delta to the low voltage distributing :conductors 7, 8v and 9i Each of' these conductors is connected to ground through a iilm cut-out ofthe type shown in Fig. 2. This cut-out comprises a metal block 19 preferably of brass' having a screwthreaded chamber in its upper side into` which lits a hollow inverted cup 20 of iiber or other suitable insulating material. The interior oi the cup 2O is filled with a conducting lliquid .21 preferably mercury which is in sulated from the brass cup 19 by a thin layer of insulating material 22 such as paper or mica. This nim of insulating material is held iii'nily between the bloclr` 19 and the in- 20 and serves to prevent electrical contact of the mercury with the block 19. A small depression 23 may be made in the block 19 immediately lbelow the insulating film into which is introduced a globule of mercury to insure a better contact between the mainA body of mercury and the block V19 when the paper :film breaks down in the manner hereinafter described. A binding screw 24 passes through the top oi the in-l sulating cup 20 and provides a means 'for making electrical contact with the mercury 21. Binding screw 25 serves to comie'ct the metal block 19 to the ground wire.

If from any cause the secondary circuit is as for instance by failure oi the insulation etween the primary `1 and thecorrespondino secondary 1, the high voltage current will. pass to ground through one or more of the iilm cut-outs 16, 17 and 18 and back to the primary circuit through one or more oi the impedance (levices 13, 14 and 15'. The passage of current through the film cut-outs will be effected by the destructionfof the ilms by the high voltage current thereby forming a permanent connection between the mercury 21 and the metal block 19. As the secondary winding 1, 2 and 3 offer a comparatively small reactance to the high voltage current the passage to ground from the secondary conductors will not be coniined to any one film cut-out, but will in general. take place through all three. Each of the coils 1 2 and 3" will then be permanently short-circuited through the ground, the consequence being an eX- ICO cessive rush of current in the primary coils of v the Atransformers and the opening of the fuses or other protective devices in the highpotential'mains thereby relieving the secondar f circuit from all danger of the high potential voltage.

In the film cut-out shown in Fig. 2, the ine sulating ilm 22 is not exposed to the atmosphere, and consequently is not subjected to deterioration from moisture or other atmos-- pheric conditions, and as the mechanical strain on the paper is dependent entirely on the weightof the column of mercury 21,

v great uniformity in 'the operation of the eutouts is secured.

tential occurs on said low potential conductors. 2. in an electrical distributing system, the combmationof high potential mains, transformers having their primariesconnected in' delta between said. mains, a 'permanent groundconnection of high impedance for each corner' of said delta, secondaries for said transformeraand means for automatically connecting said secondaries lto ground when primaryhigh potential occurs on said secondaries.

3. in an electrical distributing.systerm the combination of high potential mains, transformers having their primaries connectedin delta between said mains, a permanent ground connection of high impedance ier leach corner ci said delta, second aries for sai d transformers connected in delta, and means ier connecting said seconda-ries to ground comprising a mercury electrode and a' metallic electrode separated bya thin insulating niedium.

4. An automatic circuit closing device comprising two mercury conductors separated by a thin insulating member, and means for connecting said conductors to an electrical circuit.

5. -An automatic circuit closing device comprising two liquid conductors separated by an insulating hlm,- one of said conductors consisting of n'iercury, and means for con-v necting said mercury to an electrical circuit.

6. A circuit closing device comprising a metallic conductor, an insulating cup secured to said conductor, a thin layer of insulating material clam )ed between said cup and conductor,a1id a ody ol mercury norm ally supported by said thin layer of insulating material and insulated from said. metallic conductor.

7.- A circuit'closing device comprising a metallic block, an inverted cup of insulating material carried thereby and supporting a `column of mercury, a metal conductor passing through said cup oi insulating material and contacting with said niercury a thin layer `of insulating material lbetween said mercury and said block7 and means for connecting said mercury to an electrical circuit.

8. A film cutout comprising a metallic block having a chamber in its top, an inverted cup of insulating material screwed into said chamber, a body of mercury in said insulating cup, a paper film supporting said mercury' and normally separating it from said metallic block, and an electrical connection for said mercury through said insulating cup.

In witness whereof, l have hereunto set my hand this eighth day of September, 1904.

SAMUEL FERGUSON.

Witnesses HELEN ORFORD, G. HoLLrs'rER. 

